Microencapsulation is a process for completely enveloping tiny masses of solid particles, or liquid droplets in a protective coating which separates the substance from its environment. The use of microencapsulated chemicals for toxicology studies presents a number of advantages, i.e. it permits testing volatile or chemically reactive compounds in the animal diet, minimizes problems with palatability, etc. Volatile and/or reactive chemicals have been encapsulated using a starch, gelatin or gelatin/sorbitol matrix and determined to be stable when mixed with rodent feed. Relative bioequivalence in rats of the microencapsulated trichloroethylene, 1,1,1-trichloroethane and 2- ethylhexanol compared to the neat test material indicates no significant difference in absorption after oral administration. Palatability studies using the microencapsulated trichloroethylene, 1,1,1-trichloroethane and 2-ethylhexanol have been successfully completed. Current studies include the demonstration of bioequivalence of microencapsulated citral, cis-dichloroethylene, trans-dichloroethylene and cis/trans-dichloroethylene.